This invention relates generally to encapsulated magnet carriers and, more particularly, to encapsulated magnet carriers used in magnetically driven sealless type pumps.
A magnetically driven sealless pump is typically a centrifugal pump that has its impeller and bearing system isolated from the impeller driving mechanism by an isolating wall of a casing that seals the pumping mechanism from the surrounding environment and eliminates the necessity to use rotary seals to seal the pumped fluid against leaking along the shaft. This type of pump is particularly desirable when pumping corrosive or toxic fluids which are dangerous when allowed to leak. The driving mechanism is coupled to the pump impeller by an arrangement of magnets located on the opposite sides of the isolating wall which magnetically connects the torque of the driving mechanism to the impeller.
A magnetically driven sealless centrifugal pump typically includes an inner magnet carrier mounted on the shaft. The inner magnet carrier must be sealed against leakage and be corrosion resistant. Inner magnets are disposed in individual chambers disposed around the carrier and in contact with a conducting ring and in the arrangement of magnets located on the opposite must include an impeller bearing system which is independent of the motor driving bearings and, therefore, necessitates that the impeller bearing system carry the full load on the impeller including both radial and thrust forces.
In the past, a designer of this type of pump generally used a carrier made with an "L" cross-sectionally shaped inner piece typically made from a 316 stainless steel or an alloy casting on wrought bar stock. After the initial machining of the carrier, a circumferential row of magnets having a ferrous conducting ring in contact with block magnets are pressed onto the carrier. The conducting ring is usually machined with a three decimal place tolerance ID (inner diameter) and a flat for each block magnet on the OD (outer diameter). The flat retains the block magnet in its peripheral position. After the row or rows of block magnets are pressed in place, an "L" cross-sectionally shaped outer shield is placed over the magnets. The outer shield is made from solid wrought bar or heavy wall tubing. Investment castings were experimented with but the castings proved to be too porous. After the shield is in place, it is welded to the "L" cross-sectionally shaped inner piece at both ends of the "L" shaped shield, thus, forming a waterproof encapsulated chamber containing the magnetic blocks. When energized magnets are used electron beam welding is used for the welding. When un-energized magnets are used Gas Tungsten Arc Welding (GTAW) may be used. After the shield is welded in place, the carrier is given final welding and then balanced. This process involves many steps and includes a difficult machining of the flats on the conducting ring which is due to the small tolerances that are desired. Furthermore, welding of the "L" shaped shield at two ends of the L involve two different radii of those ends and makes the assembly more difficult to weld. Differential thermal growth can produce a shortened life span for the carrier. The L shaped shield is also costly to manufacture and weld because of its shape and required tolerances.
The foregoing illustrates limitations known to exist in present methods of manufacturing encapsulated magnet carriers. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.